1. Field of the Invention
This invention relates to a time indicator for indicating the passage of time by the appearance of, for example, a colored image and/or alphanumeric indicator. The common term for this time indicator technology is visually changing paper.
2. Prior Art
There are several commercially available time indicating systems based on the migration of a colorant or dye. In one system the colorant or dye migrates through an opaque cover or film. In another system the colorant or dye is applied to a surface in a pattern of dots of a migrating dye and a non-migrating dye and a clear film is applied over this pattern of dots. Over a period of time the migrating dye dots enlarge and develop an image which is visible through the clear film. These two technologies are, for example, covered in U.S Pat. Nos. 4,903,254 and 5,058,088, both to Haas. In both these technologies the timing is achieved by the rate of migration of the dye through layer or across a surface of the layer.
U.S. Pat. Nos. 5,633,835 and 5,822,280 to Haas, et al. adds a barrier layer to these technologies. The barrier layer is a dye impermeable layer that over a period of time permits the dye to permeate the barrier and then migrate through an opaque layer or migrate laterally. The dye impermeable layer is caused to become permeable to the dye, typically by the use of a plasticizer. Very few films dissolve with common types plasticizers. This leaves a relatively small selection of plasticizer and dye impermeable layer from which to choose. For example, a large volume of plasticizer may be needed to dissolve a thick film making the system impractical and/or expensive. Further, this system is limited to using colorants that are migrating dyes and with lateral migrating dyes, both a migrating and non-migrating dye are required.
Other related prior art:
U.S. Pat. No. 4,643,122 to Seybold describes a barrier film to control the rate of diffusion/evaporation of a solvent. Upon evaporation of the solvent, the security tag changes color indicating undesirable storage or product tampering.
U.S. Pat. No. 4,042,336 to Larsson describes a gas permeable film for a time-temperature integrating indicator. The indicator consists of a gas generating compartment, a wick and a gas permeable film, separating the two. The gas permeable film helps control the rate of evaporation.
U.S. Pat. No. 4,327,117 to Lenack, et al., utilizes an impermeable but removable or breakable barrier in a thaw indicator for frozen foods. The indicator is attached to a frozen food and when the food thaws, the components in the two segments intermix and/or interact producing a visible chemical and/or physical change. This is not used as a time indicator.
U.S. Pat. No. 4,812,053 to Bhattacharjee describes an oxygen permeable layer and an oxygen barrier used in a time-temperature indicator. The indicator is activated by physically removing the oxygen barrier. The timing is controlled by the rate of oxygen diffusion through the oxygen permeable layer.
U.S. Pat. No. 4,401,721 to Hida describes thermosensitive recording materials that have a heat sensitive layer containing leuco dyes and color formers (example: an acid) that upon heating will come together, react, and form a color. In addition to this heat sensitive layer, a protective overcoat layer may be used. The layer prevents premature or unwanted color formation. These systems change color upon heating and are not used as time indicators.
Color changing indicator agents based on changing pH have been used extensively for many years. Many of these indicators, such as phenolphthalein, have a colored and colorless pH range. Such pH indicators have been used in books, educational materials and games. For example, U.S. Pat. No. 5,215,956 to Kawashima describes a color changing print wherein, areas are printed by with different types of color changing inks that develop into different colors from their substantially invisible colorless state by reaction with a color changing agent. When an acid or base is applied by pen, marker or paintbrush, the color changing inks develop into different colors.
U.S. Pat. No. 5,085,802 to Jalinski describes a time-temperature indicator that uses a pH indicator, i.e., an acid and a base that reacts together at a certain rate and neutralizes each other. One substance is in excess of the other so that after depletion of one component, the pH changes, resulting in a color change.
U.S. Pat. No. 4,810,562 to Okawa, et al. describes a sheet wherein the image thereon changes with the application of water. In this system, an image is hidden by an opaque film. When the film becomes wet, the opaque coating layer becomes transparent revealing the hidden image underneath the opaque coating layer. This patent does not teach or suggest a time indicator unit.
U.S. Pat. No. 4,877,253 to Arenas describes a Bingo game card coated with a microporous coating. When a volatile liquid is applied to the coating that fills the micropores it makes the area to which it is applied transparent, exposing the underlying colored support sheet. This patent does not teach or suggest a time indicator unit.
U.S. Pat. No. 4,629,330 to Nichols describes a color-change indicator having a microporous layer wherein when the micropores are filled with a liquid the opacity of the layer decreases.
U.S. Pat. No. 4,229,813 Lilly, et al. describes a time indicator that does not use a barrier layer to control the timing of the indicator. This patent uses a barrier (frangible ampule) to separate the colored diffusing silicone oil from traveling up a porous strip. This barrier is physically broken by the end user to activate the timing. Timing is based on the rate of the colored oil traveling up the wick.
U.S. Pat. No. 4,163,427 to Cooperman. et al. describes containing a soluble color former micro-encapsulated in a frangible micro-capsule which is used as a freeze-thaw indicator. If the temperature decreases below the freezing point of the water solution, the ice formed causes the rupturing of the micro-capsule. Upon heating, the ice melts allowing the water and color former to flow out and produce a visual color change.
An object of this invention is to provide a non-electronic time indicating device that visually indicates the passage of a predetermined time.
Broadly, the time indicator of this invention rapidly changes color after a specific time interval. The indicator comprises a xe2x80x9cback partxe2x80x9d that includes a base substrate with a colored dye or colorant deposited on a first surface. A colorant impermeable barrier layer overlays the colorant or colored dye. The indicator further comprises a xe2x80x9cfront partxe2x80x9d that includes a substrate having an adhesive on a first surface thereof. When the back part and front part are put into adhesive contact with each other, the parts coact with each other to cause the colorant impermeable barrier layer to change to a colorant permeable layer to permit the dye to migrate through the layers to cause a color change visible through the front part.
The time indicator of this invention has an impermeable layer that prevents the colorant from appearing. The color signal does not begin to appear until the colorant impermeable barrier layer has changed to a colorant permeable layer. In one embodiment, the indicator has a migration modifier that changes the barrier layer to a permeable layer. After the barrier becomes permeable, a color appearing or color changing mechanism can occur such as, a colorant migrates to a visible layer or a colorant and co-colorant reacts/interacts resulting in a color change.
This invention may contain an opaque layer that conceals the colorant until the barrier is breached or modified.
This invention may also contain a clear front substrate with a colorant (such as a migrating dye/ink) on the back substrate.
The time indicator is supplied in two parts, which is activated by adhering the front part to the back part. The migration modifier can be in either the front or back substrate. The migration modifier changes the barrier from an impermeable layer to a permeable layer. The mechanism for the change can be performed by several methods, as discussed later.
The colorant can be: a migrating dye, a pH indicator, a leuco dye, a dye intermediate, a non-migrating dye, a reactive dye, color changing agent or any color former. The time indicator is a two step process. The first step is the breaching of the barrier layer and the second is the color appearing process.